1. Field of the Invention
This invention relates to a coil winding construction for an electric motor. More particularly, it relates to a novel improvement therein in which the safety or redundancy of each of the polyphase windings is procured by using multiple coil systems or series and in which the coils of the different series are rendered to be independent of one another to strengthen the insulation as well as to procure high fidelity in redundancy.
2. Prior Art
A number of different winding structures of the above type for the electric motors have been proposed in the art. As typical of these constructions, first and second prior-art examples disclosed in our copending Japanese Utility Model Laid Open Publication No. 7945/1988, will be described briefly by referring to FIGS. 1 to 4.
In the first prior-art example shown in FIGS. 1 and 2, the winding Uc of the U-phase is formed by a triple coil structure including three coils U.sub.1, U.sub.2 and U.sub.3, the winding Vc of the V-phase is formed by a triple coil structure including three coils V.sub.1, V.sub.2 and V.sub.3 and the winding Wc of the W-phase is formed by a triple coil structure including three coils W.sub.1, W.sub.2 and W.sub.3. There are eighteen slots .circle.1 to .circle.18 of the stator 1 and the respective slot numbers .circle.1 to .circle.18 are indicated in FIGS. 1 and 2 as being enclosed in circle marks.
Between the slots .circle.1 to .circle.18 , eighteen stator teeth 2 are formed. A rotor 5 formed integrally with the rotor shaft 4 is mounted for rotation within a rotor accommodating opening 3 provided centrally of the stator 1.
As shown in FIG. 2, six magnetized regions are formed on the rotor 5 as magnetic poles for constituting a three-phase six-pole motor.
As shown in the winding diagram of FIG. 2, coil U.sub.1, U.sub.2 and U.sub.3 of the U-phase winding Uc are wound as a bundle in a slot .circle.1 by way of a same starting slot of the winding procedure. The coils V.sub.1, V.sub.2 and V.sub.3 of the V-phase winding Vc are wound as a bundle in a slot .circle.3 by way of a same starting slot of the winding procedure, while the coils W.sub.1, W.sub.2 and W.sub.3 of the W-phase winding Wc are wound as a bundle in a slot .circle.5 by way of a same starting slot of the winding procedure.
The aforementioned phase winding Uc, Vc and Wc are initially wound at the slots .circle.1 , .circle.3 and .circle.5 and then wound in the slots .circle.1 to .circle.18 in the manner shown in FIGS. 1 and 2 to constitute the three-phase drive windings.
The above described electric motor according to the first prior-art example operates as follows:
In the state of FIG. 1, three-phase drive signals are sequentially applied to the U-phase coil Uc, V-phase coil Vc and the W-phase coil Wc, by electric switching means, not shown. Hence the rotor is driven into continuous revolutions under the magnetic interaction between the stator teeth 2 and magnetic poles of the rotor 5.
The second prior-art example shown in FIGS. 3 and 4 are proposed for improving the above described deficiencies of the first prior-art. In the following description, the parts or components same as or equivalent to those of the preceding embodiment are indicated by the same numerals of said prior-art in FIGS. 3 and 4.
A coil winding construction for an electric motor according to the second prior-art is shown in FIGS. 3 and 4, wherein the numeral 1 denotes a stator 1 formed with a number of slots .circle.1 to .circle.18 at a predetermined angular interval from one another.
Between these slots .circle.1 to .circle.18 , eighteen stator teeth 2 are formed. A rotor 5 formed integrally with the rotor shaft 4 is accommodated for rotation within a rotor accommodating opening 3 provided at the center of the stator 1.
Six magnetized regions 5a to 5f are formed on the rotor 5 to form six magnetic poles to constitute a three-phase six-pole brushless d.c. motor.
Three-phas windings Uc, Vc and Wc are wound in the slots .circle.1 to .circle.18 of the stator 1. The U-phase windings Uc are formed as a triple coil structure formed by coils U.sub.1, U.sub.2 and U.sub.3, the V-phase windings Vc are formed as a triple coil structure formed by coils V.sub.1, V.sub.2 and V.sub.3 and the W-phase windings Wc are formed as a triple coil structure formed by coils W.sub.1, W.sub.2 and W.sub.3.
Referring to the coil winding connection diagram of FIG. 4, the coils U.sub.1, U.sub.2 and U.sub.3 of the U-phase windings Uc are initially wound at the slots .circle.1 , .circle.7 and .circle.13 respectively by way of starting slot of the winding procedure and the ultimately wound at the slots .circle.10 , .circle.16 and .circle.4 respectively by way of terminate the winding procedure.
The coils V.sub.1, V.sub.2 and V.sub.3 of the V-phase windings Vc are initially wound at the slots .circle.5 , .circle.11 and .circle.17 respectively by way of a different starting slot of the winding procedure and are ultimately wouynd at the slots 12, 18 and 6 respectively by way of terminating the winding procedure.
The coils W1, W2 and W3 of the W-phase windings Wc are initially wound at the slots .circle.5 , .circle.11 and .circle.17 respectively by way of a different starting slot of the winding procedure and are ultimately wound at the slots .circle.14 , .circle.2 and .circle.8 respectively by way of terminating the winding procedure.
It will be seen from above that the coils U.sub.1 to U.sub.3, V.sub.1 to V.sub.3 and W.sub.1 to W.sub.3 of the three triple coil series of the phase windings Uc, Vc and Wc are not wound in such a manner that the three coils are accommodated simultaneously in common slots, as in the prior-art first example, but the coils are initially accommodated within different slots by way of starting the winding procedure, and that the coils in the slots .circle.1 to .circle.18 may be insulated easily and reliably.
In accordance with the construction shown in FIGS. 3 and 4, the winding state of the coils U.sub.1 to U.sub.3, V.sub.1 to V.sub.3 and W.sub.1 to W.sub.3 of the single, double and triple systems in the three phases U, V and W is schematically shown.
In the above construction, three phase driven signals are sequentially applied to the U-phase coil Uc, V-phase coil Vc and to the W-phase coil Wc, by means of electronic switching means, not shown, such that the rotor 5 is driven into continuous revolutions under magnetic interactions between the stator teeth 2 and the magnetic poles 5a to 5f of the rotor 5.
In the first prior-art example shown in FIGS. 1 and 2, the coils U.sub.1, U.sub.2, U.sub.3, V.sub.1, V.sub.2, V.sub.3 and W.sub.1, W.sub.2, W.sub.3 of the phase windings Uc, Vc and Wc, wound triply for assuring the safe operation, are initially wound in the slots .circle.1 , .circle.3 and .circle.5 as bundles, such that the three coils are insulated as one unit in the independent state, using slot insulations and coil end insulations. Therefore, when the insulating properties of the insulators are deteriorated under thermal effects, for example, the three coils arranged as a triple coil structure may be shorted simultaneously to lower or imperil the operating reliability.
In the second prior-art example shown in FIGS. 3 and 4, an improvement is achieved in assuring insulating properties as compared with the construction of the above described first prior-art example. However, as shown in FIGS. 3 and 4, the windings are not independent for each of the coil series and are partially overlapped with one another in the course of winding. The result is that the insulation between the windings is not complete and, in case the insulating properties are lost, redundancy can be assured only with considerable difficulties.